Radio telegraph system



Jan. 1932- E. E. KLEINSCHMIDT RADIO TELEGRAPH SYSTEM Filed April '7. 192B 3 Sheets-Sheet l A TTORNEY.

Jan. 26, 1932. E. E. KLExNscHMmT 1,842,721

RADIO TELEGRAPH SYS TEM Filed April 7, 1928 3 Sheets-Sheet 3 \o XGDGD Q q IN VEN TOR A TTO PJVE Y.

Patented Jan. 26, 1932 UNlTElE STATES PATENT OFFICE EDWARD E. KLEINSCI'IMIDT, OF CHICAGO, ILLINOIS, ASSIGNOR 'IO TELETYPE CORPORA- TION, OF CHICAGO, ILLINOIS, A. CORPORATION OF DELAWARE.

RADIO TELEGRAPH SYSTEM Application filed April 7,

lrly invention relates to signalling systems and is particularly adapted for use in radio printing telegraph systen'ls. In operating a printing telegraph over a 'adio transmitting system ditlicultics inherent in this class of signalling systems have been experienced which have retarded. its active development. Thus for example, as is well known, only a comparatively small amount of energy is transmitted by radio and accordingly there are occasional failures in the operation of relay devices employed in printing telegraph systems due to this comparatively large ener: v requirement. This difficulty is amplified 1 by the radio phenomenon known as fading,

which may, if occurring during signalling periods, cause the loss of an impulse and thereby the mut-ilating of the transmitted code.

Another difficulty which has been experienced in such s stems is the effect of static which may come unheralded at any time during the signalling period and so distort and mutilate the signals resulting in false operation. of the receiver.

An object of my invention therefore is to provide a radio printing telegraph system which overcomes these diiliculties.

A. further object of my invention is to provide a radio frequency tuned printing telegraph system in which the receiving printer operates solely under local power controlled from the transn'iitting end.

in. general, the invention contemplates circuit arrangements at the receiving end of the system arranged to control a printer in ac cordance witl alternate marking and spacing signal conditions while no signals are being rectived from the transmitting stations, the receiver circuit being responsive to a received signal to prevent further alternate marking and spacing operations. The printer thereupon operates in. accordance with either marking or spacing conditions depending on which of these the printer last responded.

1928. Serial No. 268,238.

As is evident, inasmuch as this type of control employs only the negative operation of stopping a local action, it will require considerably less received energy therefor than is required in the present systems which at tempt to operate relays in a positive manner in accordance with received signals.

Referring to the drawings-- Figure 1 is a diagram of the circuit connections and apparatus employed at the transmitting end of the telegraph system and Figures 2 and 3 show a diagram of the apparatus and circuits employed at the receiving end of the system.

Referring to Figure 1, a radio telegraph transmitting station A is shown comprising my improved form of transmitting apparatus l electrically connected by a transformer 2 to a radio frequency oscillating circuit 3.

The transmitting apparatus 1 includes a three element tube 4 of a suitable construc tion comprising a heated filament, grid and plate, the grid of the tube 4 being normally negatively biased by the battery 5 to prevent a flow oi current in the plate circuit of the tube. The positive terminal of the battery 5 is connected to one plate of the condenser 6, the other plate of which is connected over the conductor 7 to the negative side of the bat tcry 9. The plate of the vacuum tube 4 is connected over the conductor 10 to a winding 11 the circuit of which is in turn completed over conductor 12 to the midpoint of the battery 9. i

'l he vacuum tube 13 of construction similar to the tube 4 is likewise provided. with a grid which is normally negatively biased by the battery 14 to prevent a flow of current in the plate circuit under normal conditions. The positive terminal of the battery ll is connected to one plate oi the condenser 15, the opposite plate of which. is connected to the midpoint of the battery 9. The plate circuit of the tube 13 is connected over conductor 16 to Winding 17 the opposite terminal of which is connected to the positive side of battery 9. The windings 11 and 17 comprise a relay 18 controlling the operation of armatures 19 to 21. Armature 19, it will be noted, is connected over the conductor 23 to one side of condenser 6 and the contact engaged by the armature 19 is connected over conductor 24 to the opposite side of the condenser 6 and the battery 5. Armature 21 is connected over conductor 25 to one side of condenser 15 and its engaging contact is connected over conductor 26 to the opposite side of the condenser. These two armatures 19 and 21, which, it will be understood, are mechanically connected to each other so that they move as a unit, function in a manner to be described in detail hereinafter to alternately open and close bypass circuits for their respective condensers 6 and 15, whereby these condensers are alternately charged and discharged at a low or telegraph signaling frequency. Armature 20 is connected over the conductor 27 to the battery 28. Armature 20 operates betweenits two contacts connected to conductors 29 and 30 respectively connected to marking and spacing contacts of the single contact transmitter 31.

The transmitter 31 is operated in accordance with a predetermined code under control of a tuning fork 33 secured to a fixed support 34: and is provided with tines 35 upon which are secured adjustable weights 36 for the purpose of regulating the vibration frequencies of the forks to maintain synchronism with the electrical oscillating circuits including tubes 1 and 13 described above. Secured to the tines 35 are insulated contacting members 37, which, as the tines 35 spread and come together, permit its contacts to open and close. Connected in series with these contacts is a magnetic drive magnet 33 for controlling the vibration of the tines 35. To start the fork 33-into vibration the tines 35 are stretched by hand and released. The movement of the tines outward, closes a cir-- cuit through the magnet 38 over the contacts 37 and the battery 9. Energization of the magnet 38 attracts the tines and draws them inward. As the tines move inward, contact 37 separates to open the circuit and de-energize the magnet 38. In this manner the fork is kept in vibration at a uniform and predetermined rate of a frequency equal to the operation of the oscillating circuit. Contact operating member 39 secured to the tines 35 of the tuning fork 33 opens and closes its contacts 40 connected to the electrical circuit of the magnet 11. Magnet ll as it alternately energizesand de-energizes, operates an e capement wheel 43 secured to the pin barrel shaft 44: of the transmitter 31. As the tuning fork 33 vibrates in the manner described above, the pin barrel 4% is stepped around in unison or synchronism with the operation of the oscillation circuit described above. As

described in the Patent 1,567,599 to Kleinschmidt issued December 29, 1925, the cont actor 31 is moved from one to its alternate contact in accordance with the code set up as the pin barrel rotates to transmit impulses by modifying the train of oscillations set up in circuit 3 in a manner to be described in detail hereinafter.

Operation The operation of the apparatus thus far described is as follows:

lVith the apparatus and circuits in the condition shown, the condenser 6 is receiving a charge from the left portion of the battery 9 over circuit including the conductor 7 through the condenser and through the resistance 22. Resistance 22 prevents an electrical on the condenser when the latter is connected across the battery or when discharged in the manner to be described. As the condenser 6 receives the charge from the bat- ,ery 9, its potential approaches that of the battery minus the drop in resistance 22sufficient to overcome the negative bias of the grid battery 5., The potential of grid tube 1 accordingly becomes positive with respect to the filament and current flows in the plate circuit of the tube through the winding 11 to the mid-point of battery 9 over conductor 12 and thence through the battery to the filament of the tube 4:. As a result of the energization of winding 11 over the circuit traced above, the armatures 19 to 21 are moved from their right hand position shown to their opposite or alternate position and armature 19 as a result engages its contact. As a result of the engagement of the contact by armature 19, the condenser 6 is short circuited over the conductors 23 and 24 through armature 19.

The condenser 6 will accordingly discharge over this circuit and the bias of the battery 5 will again be sufficient to prevent further flow of current in the tube 1. Short circuit of battery 9 is prevented at this time by resistance 22.

Simultaneously, the condenser 15 which is shown in the drawings, as short circuited over the conductor 26, armature 21, and conductor 25 will now be charged due to the fact that the armature 21 no longer is in engagement with its contact, the charging circuit being completed from one plate of the condenser 15 and through the resistance 32. Condenser 15 receives a charge from the battery 9 and its voltage approaches that of the charging portion of a battery 9. This voltage is sufficient to overcome the negative bias of battery 1 1 and current will thereupon flow in the plate circuit of the tube 13. With current flowing in the plate circuit over conductor 16 through the winding of relay 17 to battery 9 and the filament of tube 13, the winding 17 is energized and the armatures 19 to 21 are moved to their positions in engagement with their left hand contacts to the position shown in the drawings. The same cycle of operations is thereupon repeated. Current flows through the windings 11 and 17 alternately and the armatures 19 to 21 move between alternate positions.

The transmitter contact 31 is connected over a conductor 4E6 through a relay winding ll, the other terminal of which is connected to battery 2?. Relay at? includes armature l8 connected over the conductor to the midpoint of the battery 9 and armature 49 com ncctcd over the conductor 51 to the negative side of the battery 9. The engaging contact of armature 48 is connected over conductors 52 and 26 to the spring]; contact of armature 21 and the spring; contact of armature 49 is connectedover the conductors 53 and i l-l: to the spring contact of armature 19.

Normally as the armatiu'e 20 vibrates between its two contacts, and the receiver printer is to be operated in accordance with alternate marking and spacing operations, the transmitter contact 31 in accordance with a code combination to be transmitted in the manner described in the above referred to patent, moves between its contacts engaging the contact connected to conductor 30 at the instant when the armature 20 is in engagement with the contact connected to the con ductor 29. Similarly upon the succeeding operation, contact 31 engages the contact connected to a conductor 29 at the instant when armature 20 is connected to conductor 30.

in this manner during; alternate marking and spacing rwriods, no circuit is completed over either cmuluctors 29 or St) and conductors at; and 2 and relay 4t? therefore remains dc-cucrtrizcd under normal. conditions.

ll hcn. however. a marking impulse is to he followed by a marking: in'ipulse or a spacinn impulse succeeds a spacing" impulse, the transmitter contact 31 is maintained in en- ;Iaucmcnt with one contact for successive signal periods and as the armature 20 moves to its alternate position, an (meratiug circuit is couuilcted. As shown, if a contactor 31 were maintained in position as shown, a circuit is completed ovcr the conductor 30, contactorfll, and (-ondiuztor 46 through the wind ion; of the relay at? through battery and conductor to arn'iature 20. The relay l-.7 energizes to more its armaturcs il-S and 4-?) into their contact engaging: position Upon the movement of armature t8 into e1 nent with its con tact. a bypass circuit is completed for the condom-'1' 15 over the conductor 50. armature l-El and its front contact and conductor 52. .Fliniilarly, armature d9 (Imaging its front contact completes a by-pass circuit for the condenser (5 over the cm'idnctor 51 armature 4S) and its front contact and conductor 53, and as a result neither the condenser 6 nor the condenser-1.5 can be charged at this time. T he electrical operating circuit described above,

is thus brought to a stop for the purpose to be described in detail hereinafter in connection with the receiving station.

7 Connected in multiple with the winding 47", over conductors 46 and 27 is the primary winding 55 of the transformer 2. The secondary winding 56 is connected in a tuned circuit including condenser 57 connected to the input side of a three element tube 58. In the out-put circuit of the three element tube 58, a variable condenser 59 and inductance 60 are connected providing a radio-frequency tuned circuit. This circuit is connected to the primary winding til of a radio frequency transiormcr (32, the secondary 63 of which is connected in the antenna circuit The operation of the tuned circuit 8 including the three element tube 58 and tuned input and output circuitis well known in the art and need not be described in detail here. As is well known, when a circuit is completed for the primary winding 55, oscillations of radio fretpiency in the oscillating circuit of the vacuum tube 58 are started which are radiatcd over the circuit (lei. Normally there fore as the transmitter contact 31 operates between its contacts during; marking and spacin intervals, and no circuit is completed through winding55 as described above, no energy is radiated. W hen, however, the transmitter contact 31 is operated in response to succc nve marking impulses for example, a circuit is completed for the relay winding 4? and for the primary transformer winding 55 in parallel therewith and current in the secondary oscillating circuit 56 is set into oporation to radiate a radio frequency signal.

The receivingapparatus, Figure 2 includes a receiver for rot-solving the radio signals transmit-ted from station A connected to a coupling coil 71,, the secondary of which is ccmncctod in the input of a radio frequency amplifier tube 72. The output of the amplifier tube 72 in turn is connected through a radio frequency trai'isformcr 73 to a second stage radio fretniency amplifier tube 73'. The tubes 72 and 73 are connected in the well known manner for neutralizing their coupling; capacity by means of the condensers 74. 75. and 76. 'i 1e couplingcapacity inherent between tuned circuits is due to the capacity between the grid and the plate of the vacuum tubes and also between the radio frequency transformers 71, 73 and 77 and their respective condensers 78, 79, and 80 are thus balanced. The detailed operation of the neu tralizinn' circuits has been fully discussed in the art and in many patents and therefore need not be described here. The adaptation of this circuit in the manner herein described for special printing telegraph systems has not, however. been heretofore disclosed and forms part of applicants invention.

As is well known when a circuit is properly neutralized, the degree of amplification of the received signals without signal distortion may be considerably increased over that possible with an ordinary radio frequency tuned circuit. By this arrangement, therefore received telegraph signals may be considerably amplified before reaching the operating circuit. The secondary winding of transformer 77 is connected to the input side of a detector tube 82, the output circuit of which is in turn connected to a radio frequency transformer 83 connected in turn to the input of amplifier and detector tube 84.

Resistance 85 (Figure 3) connectedacross the out-put of the amplifier and detector tube 84, is connected by means of conductor 86 to the filaments of the two vacuum tubes 87 and 88. The resistance 85 thus acts as a resistance coupling between the tube 84 and the tubes 87 and 88. The opposite terminal of the resistance 85 is connected over the conductor 89 to the armature 90 controlled by the relay 91. The armature 90 operates between contacts connected to the conductors 92 and 93 respectively, the conductor 92 being connected through the grid of the vacuum tube 88 and the conductor 93 to the grid of vacuum tube 8 The relay 91 comprises windings 92 and 93 and armatures 94, 95 and 96 in addition to the armatures 90 described above. The armature 94 operates between contacts connected to conductors 97 and 98 respectively, the conductor 98 being connected to the plate of tube 87 through the battery 99 and the conductor 97 4 being connected to the filament of tube 87.

The armature 95 operates between contacts connected to conductors 100 and 101 respectively. The conductor 100 is connected to the plate of the tube 88 through the battery 102 and conductor 101 is connected to the filament of this tube. Conductor 97 is connected to one plate of condenser 103, connected across the input of tube 104, the grid of which is normally negatively biased by battery 105. Armature 94'is connected to the opposite terminal of condenser 103 over the conductor 106. The winding 92, it will be noted, is connected to the plate circuit of the tube 104 through the battery 108.

The conductor 101 is connected to one terminal of the condenser 109 connected across the input of the vacuum tube 110 which is normally negatively biased by the battery 111. The armature 95 is connected over the conductor 112 to the opposite terminal of the condenser 109. In the output circuit of the vacuum tube 110 is the winding 93 of the relay 91 connected to the filament of the tube 110 over conductor 101. The armature 96 altelnately engages and disengages its contacts in the manner to be described hereinafter and alternately opens and closes the circuit for the operating relay 115 through the battery 116. i

Theoperating magnet 115 operates a pin barrel or cam shaft 117 of areceiving printer as shown in the copending application b'er. No. 741,578 filed October 4, 1924, which has now matured into Patent 1,758,194, granted May 13, 1930, in accordance with received impulses. The pin barrel 117 is rotated by an escapement wheel 118 mounted upon and controlling the shaft 117. As escapement mechanism 119 actuated by the magnet 120 operates the escapement wheel 118. The mag- 11et'120 is connected in an electrical circuit with insulating contactor 121 secured to the tines 122 of a tuning fork 123. The tuning fork 123 is secured to a fixed support 124 and is provided with adjustable wei hts 125 for the purpose of regulating the vi rating frequency of the fork. A magnet 126 connected to the insulated contact member carried on the tines 122 maintainsthe forks in vibration. These forks are started by first spreading the tines 122 by hand, then by releasing them. When the tines spread, a circuit is completed for the magnet 126 from the battery 127 and magnet 125 is energizing to bring the tines together. As the tines spread and come together a circuit is completed for relay 120 to stop the-pin barrel 117. The frequency of tines 122 equals, of course, that of the tines 35 at the transmitter station so that pin barrels 44 and 117 are rotated in synchronism.

No specific means for maintaining these forks in synchronism is disclosed although it will be understood that any well known form of synchronizing may be employed such as a separate synchronizing carrier frequency.

The operation of the apparatus at the receiving station, thus far described, is as follows:

When no signals are being received, the tube 84 is normally negatively biased and no current flows in its plate circuit to the resistance 85. With the apparatus in the condition shown, a circuit is completed for charging the condenser 109, from one side of the condenser 109 through the filament of the tube 88 to the plate thereof, battery 102, conductor 100 over the upper contactand armatu're 95 and conductor 112 to the opposite terminal of the condenser 109. Suflicient current flows through the tube 88 to charge the condenser 109 and this condenser is finally so charged that its voltage overcomes the negative bias of the battery 111, which heretofore has prevented the flow of current in the plate circuit as described above. At this time no charge can accumulate on the condenser 103 by reason of the short circuit around this condenser over conductor 106, armature 94 and its upper contact and the conductor 97. This short circuit discharges the condenser 103 of any charge which may have accumulated therein, while at the same time a charging circuit therefor is opened at armature 94.

After an interval of time equal to the predetermined signalling period, the condenser 109 receives a suilicient charge to overcome the voltage of the negative biasing battery 111 and current flows in the plate circuit of the tube 1l0, the circuit being traced through the battery 118, winding of 93, conductor 101 to the filament of the tube 110. As a result, the winding 98 energized and operates the ari'natures 90, 9d, 95 and 90 to their opposite contacts. As a result of the armature 9: moving to engage its lower contact, the charging circuit for condenser 109 traced above opened and instead a discharging circuit is completed therefor over the lower contact of arn'iature 95. As a result the negative bias of battery 1 11 again prevents flow of current in the plate circuit of the tube 110. As a result of the engagement of armature 9dand lower contact, the short circuit for the condenser 103 is opened and a charging circuit therefor is completed from one plate 01' the condenser 103 adjacent to the filament oi? tube 87 to the plate thereof over battery 00, conductor 98, lower contact and armature 9 1, and over conductor 100 to the opposite plate oi? the condenser 108. Suthcient current is passed through the tube 87 to charge the condenser 103 and after an inter val 01 time this condenser is suiiiciently charged so that its voltage overcomes the negative bias of the battery 105..

As a result current flows in the plate circuit of the tube 1041 through battery 108,

winding of the relay 92 over coin'luctor 97, to

the filament of the tube, and the armatures 00 and 94 to 96 are moved to engage their alternate contacts. in this manner while no current is flowing in the resistance 85 due to the normal biasing oi": the amplifier tube 8 1,

as described above, the local circuit including the tubes 87, 88, 104%, and 110 operate to alternately energize the windings 02 and 93 and move the armatures to their alternate contacts successively and as the armature 96 is operated, it alternatelyopens and closes the circuit for relay 11.5.

l Vhen, however, a signal is received from the remote transmitting station A due to an operation of the transmitter 31., the resultant current flowing in the plate circuit of tube 82 in the manner already described overcomes the negative bias of the amplifier tube 84; and current accordingly flows in the plate circuit and through the resistance 85. As a result of the current flow in resistance 85, a negative potential is impressed on the grid of the succeeding tubes 87 or 88 biasing the grid oi? either of these tubes negatively depend.- ing on which of these is in the operating circuit at the time. As a result of this negative bias produced by the current flow in the resistance 85, the plate of either of these tubes 87 or 88 will not draw current.

It will be assumed for the purposes of illustration thatthe signal is received at the instant when the armatures are in the posi tion shown. As described above, the condenser 109 is at this time about to be charged by the current flowing through the tube 88 and condenser 103 is short circuited at armature 9 1-. inasmuch, however, as current flowing through the resistance 85 now produces a negative bias on the grid of the tube 88 the connection for the resistance 85 being made over conductor 89, armature 90 and conductor 92 to the grid of tube 88, no current can flow in the plate circuit of the tube 88 and accordingly condenser 109 will not be charged in the normal manner and the tubes 110 and 104 will both remain negatively biased and therefore non-operative so that no current flows through either the winding 92 or t 3. The armatures will therefore re main in their last set position, that is, in the position shown. If this continues for one signal period, the printer magnet 115 will remain deenergized in accordance with two successive spacing intervals as the armature 90 is at this time 111 its open position. At the end of the signal interval, the charging circuit for the condenser 109 will again become el'iective and this condenser will become charged in the manner already described above, the circuits including tubes 87 88, 104, 110 as described above.

It will be evident from thisdescription that the actual operating signals are generated at the receiving end by the oscillating circuits including the tubes 87 and 88,104 and 110 and that the operations depend solely upon the small amount of energy necessary in raising the potential of the resistance 85 sufiiciently to produce a negative bias on either the tubes 87 or 88. Since to produce such a negative bias requires merely voltage and substantially no flow of current, it is evident that the actual energy that need be transmitted may be minute. By applying the principle of neutralization, these currentsmay be amplified and accordingly the ope 'ations of the systems is substantially unaffected by fading. Since theoperation depends on a substantial potential variation of a particular character, static will have substantially no injurious effects on the system.

By employing tuned circuits, the oscillations of the transmitter and receiver can be maintained in synchronism by the inherent characteristics of the condensers and inductances comprising the circuits. It will be evident therefore that windings 17 and 92, will operate simultaneously as will windings 11 and 93.

Although I have shown my invention in connection with a specific radio system, it is evident that it has a much broader application including any system in which received signals exercise a negative control and I do not intend to limit myself by the specific arrangcment disclosed.

I claim:

1. In a radio telegraph system, a transmitting station, a receiving station, means including a transmitter at said transmitting station for transmitting code combinations of impulses to said receiving station, said means being normally in a non-operating condition, a printer at said second station, a receiver at said second station operated while said transmitter is in its normal condition and is not transmitting any code, for operating said printer in accordance with alternate marking and spacing impulses, said means at said transmitting station operating to transmit code combinations of impulses to said receiver, means at said receiving station responsive to said received code combinations of impulses for stopping the normal alternate marking and spacing operations of said printer and operating said printer continually in accordance with the last either markingorspacing operation which preceded the receipt, of the signal.

2. In a printing telegraph system, a transmitting station, a receiving station, an oscillator at said transmitting station, said oscillator being normally in non-operating condition, a printer at said receiving station, means including circuit connections to said printer for normally operating said printer in accordance with marking and spacing impulses, means at said transmitting station for rendering said oscillator operative to radiate energy, said circuit connection means at said receiving station being responsive to said radiated energy for stopping the normal operation of said printer and operating said printer continuously in accordance with the operation performed thereon just preceding thereceipt of said oscillation. In a radio printing telegraph system, a printer, a receiver circuit normally operating at a signalling frequency and connected to said printer to operate said printer alternately in accordance with marking and spacing operations, and a radio receiving circuit responsive to received impulses for rendering said oscillating circuit non-operative whereby said printer continues to operate in accordance with the operation last performed thereon before the receipt of said frequency.

4. In a radio telegraph system, a receiver, comprising a radio frequency tuned circuit, a three element detector tube, the grid of which is normally biased to prevent current flow in the plate circuit, a telegraph circuit operating at telegraph frequency connected to said detector, said detector tube being responsive to carrier currents received through said radio frequency tuned circuit whereby current flows in its plate circuit, said telegraph circuit being rendered non-operative responsive to said current flow in the plate circuit of said detector tube.

5. In a radio telegraph receiver, a tuned radio frequency circuit, a detector tube comprising a normally negatively biased grid to prevent the flow of current in its plate circuit during normal non-operating conditions, said detector tube being responsive to a received radio frequency through said frequency tuned circuit for overcoming the bias of said negative grid whereby current flows in its plate circuit and a telegraph circuit connected to said detector tube operating at telegraph frequency while no current flows in the plate circuit of the detector tube and rendered nonoperative responsive to current flow in the plate circuit for preventing the operation of said telegraph circuit.

6. In a radio telegraph receiver, a tuned radio frequency circuit, a three element detector tube comprising a normally negatively biased grid to prevent the flow of current in its plate circuit during normal non-operating conditions, said detector tube being responsive to a received radio frequency through said radio frequency tuned circuit for overcoming the negative bias of said grid whereby current flows in the plate circuit, a telegraph circuit connected to said detector tube operating at telegraph frequency while no current flows in the plate circuit of said detector tube and rendered non-operative in response to current flow in the plate circuit, and a )rinter controlled by said tuned telegraph circuit to alternately make marking and spacing operations while said circuit is in operation and continuous marking or continuous spacing operations when said circuit is rendered nonoperative.

7. In a printing telegraph system, a transmitting station, a receiving station, a transmitter at said transmitting station for transmitting code combinations of marking and spacing impulses, a source of alternating current at said transmitting station, said transmitter being connected to said source of alternating current for controlling said alternating current in accordance with 7 code combinations of marking and spacing conditions, means for conducting said alternating current modified in accordance with the operations of said transmitter to said receiving station, means whereby no current is conducted during normal successive marking and spacing conditions, a printing magnet at said receiving station, means for operating said printing magnet alternately in accordance with marking and spacing impulse conditions while no currents are being received from said transmitting station and means at said receiving station connected tosaid printer and responsive to said currents during periods when successive marking or spacing conditions are part of the code combination for varying the operation of said receiver.

8. In a printing telegraph system, a transmitting station, a transmitter t-hereat for transmitting code combinations of marking and spacing conditions, a source of alternating current connected to said transmitter whereby said alternating current is controlled in accordance with the operation of said transmitter current being transmitted only when successive marking or spacing conditions make up the code combination, a re ceiving station, a printer thereat, means whereby said printer is operated in accordance with alternate marking and spacing con ditions While no impulses are being received from said transmitting station and means responsive to a received impulse from said transmitting station for modifying said operation of said receiver.

9. In a telegraph system, a transmitting station; a receiving station; a telegraph frequency oscillating circuit at each of said stations; a tuning fork at each of said stations; a transmitter at said transmitting station operated by said tuning fork and said telegraph frequency circuit thereat; a source of alternating current connected to said transmittcr whereby said alternating current is controlled in accordance with the operation of said transmitter; and a receiver at said receiving station operated by said tuning tor-k and said telegraph frequency circuit thereat in accordance with the received alternating current.

In testimony whereof I afiix my signature.

EDWARD E. KLEINSGHMIDT. 

